Updated November 1, 2026

San Diego's tap water is very hard. Here's why, and what's changing

The city of San Diego serves about 1.4 million people and imports most of its water from hundreds of miles away. That's why kettles scale up so quickly here: the water starts out mineral-heavy, and local treatment doesn't soften it.

By the numbers, from the 2025 report

• 237 ppm (13.8 gpg) average hardness at the Alvarado plant, 242 ppm (14.1 gpg) at Miramar and 243 ppm (14.2 gpg) at Otay.
• 145 ppm (8.5 gpg) in the purchased treated water, with a wide range of 54–232 ppm.
• 86–111 ppm average sodium at the three city plants.
• 0 of 56 homes in the most recent lead and copper study above the lead action level. The 90th-percentile result was not detected.
• 72 treatment-plant samples analyzed for lead in 2025, in addition to the tap study.

Mostly imported, treated locally

San Diego doesn't have the rivers or aquifers to supply itself, so most of its water is imported through the San Diego County Water Authority. The report describes that imported water as mostly a blend of Colorado River and State Water Project supply. The city treats it alongside runoff captured in local reservoirs. Less than 10% of the water bought from the Water Authority arrives already treated, as a blend from Metropolitan's Skinner plant, the Authority's Twin Oaks Valley plant and the Carlsbad Desalination Plant.

The city's local reservoirs and watersheds include El Capitan, Murray, San Vicente, Sutherland, Barrett, Morena, Otay, Upper Otay, Hodges and Miramar. The city surveys them at least every five years. The 2025 survey named wildfire runoff, erosion and geological fault activity among the potential contamination sources, which is a reminder that in Southern California, fire season is also a water quality issue.

Ozone at two plants, chlorine dioxide at the third

Alvarado and Miramar use ozone as their primary disinfectant, and Otay uses chlorine dioxide. All three run conventional treatment: coagulation, flocculation, sedimentation and filtration through anthracite coal and sand. Chloramine (chlorine plus ammonia) is added to protect the water in the pipes, and fluoride is added at the plants. The city credits these advanced disinfection methods with better-tasting water. The chloramine residual still matters if you keep fish.

Pure Water: a local supply in 2027

The city's largest infrastructure project, Pure Water, will purify recycled wastewater into drinking water. The 2025 report says Phase 1 construction was about 90% complete, with deliveries expected to begin in early 2027. The city's stated goals are a reliable local supply and less treated wastewater discharged to the Pacific. Highly purified water carries very little mineral content, so it could eventually pull hardness down in the areas it reaches. The report doesn't give a figure for that, so treat it as a possibility rather than a promise.

Living with very hard water

At roughly 14 gpg, scale builds quickly in tank water heaters, dishwashers and espresso machines. If you're deciding between a softener, a scale-reduction cartridge or simply descaling more often, start with the cost math in our softener sizing calculator and the salt cost calculator. The sodium figures belong in that decision too. A salt-based softener exchanges hardness for more sodium, and San Diego water already starts at around 86–111 ppm, so anyone on a low-sodium diet should talk to their doctor or use potassium chloride instead.